Press [Esc] to pause the game. Then, press C and 
type one of the following codes at the password 
prompt to activate the corresponding cheat function. 
If you entered the code correctly, the word 
"Outstanding" will be spoken.

14214 - Invincibility
13593 - Maximum fuel and armor
25245 - Maximum weapons
17357 - Mission select   
33124 - All missions completed